Multilayer films have been utilized for the packaging of "oxygen-sensitive products", such as lettuce, i.e., products which exhibit lower shelf life in the presence of either too much oxygen in the package, or too little oxygen in the package. In such multilayer films, the O.sub.2 -transmission rate, and even the CO.sub.2 -transmission rate, are of primary importance, especially in the packaging of such O.sub.2 -sensitive products as vegetables, fruits, and cheese. For example, in the packaging of precut lettuce, the presence of too much O.sub.2 in the package results in an enzymatic browning of cut surfaces, known as pink ribbing. On the other hand, if the concentration of O.sub.2 in the package is too low, the lettuce tends to spoil due to anaerobiosis.
One of the commercially-available multilayer films which has been used in the packaging of oxygen-sensitive products has an outer heat-resistant layer of an elastomer, such a styrene-butadiene copolymer, and an outer sealant layer of a metallocene-catalyzed ethylene/alpha-olefin copolymer. Although this multilayer film exhibits desired O.sub.2 and CO.sub.2 transmission rates, as well as a desirable stiffness, this multilayer film has been found to exhibit an undesirable level of "curl," thereby exhibiting less-than-desired machinability performance. In form-fill-and-seal machinery ("FFS" machinery), curl causes film threadup problems as well as film tracking problems. Furthermore, in FFS packaging, the presence of the outer heat-resistant elastomer layer restricts package formation to a fin-type backseal, as the metallocene-catalyzed outer film layer does not seal well to the heat-resistant elastomer layer.
It has also been found that there is a pervasive belief among many skilled in the packaging of a variety of products that a heat seal cannot be made using a film having both outer layers of a low melt point polyethylene-based polymer, i.e., including both polyethylene homopolymer as well as ethylene/alpha-olefin copolymers, as it is believed that the hot bar will tend to stick to the film during sealing.
It would be desirable to provide a film which exhibits desirable O.sub.2 and CO.sub.2 transmission rates and a desirable stiffness, while reducing or eliminating the curl of the film, as well as providing a film which is suitable to a lap-type backseal for FFS packaging, using constant heat as opposed to impulse heating. Since fogging of the package is also a common problem in the packaging of produce and other food products, it would also be desirable that the film resist fogging, in order to provide the consumer with a clear view of the contents of the package, and in order to provide a more aesthetically appealing package, especially in retail applications where product presentation is important. However, those surface active agents which are effective antifog agents tend to interfere with ink adhesion to the film. This detrimental effect occurs because the antifog agent blooms to the outside surface of the package and interferes with the adhesion of the ink to the film. This detriment is significant for packages designed for consumer end use, as the consumer does not find such a package to be appealing if the ink is smeared or if the ink comes off onto other articles or the consumer. Thus, it would be also desirable to provide the film with an antifog agent on an outer film surface which forms the inside surface of the package, while also providing adequate adhesion for printing on an outer surface of the film, which outer surface serves as the outside surface of the package.